A refrigeration system is employed to cool a mix in a frozen dessert system. The frozen dessert system typically includes a hopper which stores the mix and a freezing cylinder that cools and adds air into the mix prior to serving. The freezing cylinder is cooled by a refrigeration system. Refrigerant is compressed in a compressor to a high pressure and a high enthalpy. The refrigerant flows through a condenser and rejects heat to a fluid medium and is cooled. The high pressure and low enthalpy refrigerant is then expanded to a low pressure. The refrigerant flows through tubing encircling the freezing cylinder and cools the mix in the freezing cylinder. The low pressure and high enthalpy refrigerant returns to the compressor, completing the cycle.
The hopper is cooled by a separate glycol system including tubes that wrap around both the hopper and the freezing cylinder. The glycol first flows around the freezing cylinder and is cooled. The cooled glycol then flows around the hopper to cool the mix in the hopper. To meet food safety standards, the mix in the hopper is generally maintained below 41° F.
The mix is heat treated every night to kill any bacteria. The mix is heated for approximately 90 minutes to a temperature of at least 150° F. The mix is maintained at a temperature over 150° F. for 30 minutes and then cooled to 41° F. within 120 minutes. The mix is heated by heating the glycol with an electrical resistance heater or a gas burner. The heated glycol flows around the hopper and the freezing cylinder to heat the mix.
A drawback to this system is that the freezing cylinder and the hopper are coupled by the glycol system. When the cooled glycol flows around the hopper during cooling, the glycol is heated. The heated glycol then flows around the freezing cylinder, which can melt the mix in the freezing cylinder.
During heat treatment, the glycol first heats the mix in the freezing cylinder. The glycol is cooled and therefore less effective in heating the mix in the hopper. It takes longer to heat the mix in the hopper, possibly increasing the length of the heat treatment cycle to over three hours. The heat treatment cycle can change the flavor of the mix, and a longer heat treatment cycle can negatively affect the flavor of the frozen dessert.
In prior hot gas heat treatment systems, the mix in the hopper and the freezing cylinder cannot be separately cooled. If one of the hopper and the freezing cylinder required cooling, the other has to be cooled as well. The suction lines of the hopper and the freezing cylinder of the prior art system are coupled, and therefore it is difficult to vary the pressure, and hence the temperature, of the refrigerant flowing around the hopper and the freezing cylinder. It is preferably for the refrigerant cooling the mix in the hopper to have a different temperature and pressure than the refrigerant freezing the mix in the freezing cylinder. Another drawback of the prior art hot gas heat treatment system is that the system has a low capacity, and therefore the compressor is undersized to attain compressor reliability.